Comparison of Polar Ozone and Aerosol Measurement (POAM) II and Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol measurements from 1994 to 1996

Abstract

We describe statistical comparisons between version 6.0 Polar Ozone and Aerosol Measurement (POAM) II and version 5.931 Stratospheric Aerosol and Gas Experiment (SAGE) II measurements of aerosol extinction and derived surface area and volume density between 1994 and 1996. Qualitatively, both instruments show similar decay of the aerosol extinction at visible and near‐IR wavelengths in the altitude range from 12 to 30 km, resulting from dissipation of the Mount Pinatubo aerosols. We present quantitative differences between the SAGE II and POAM II extinctions at 1 and 0.45 μm for temporally and spatially coincident measurements. On average, for the moderately elevated aerosol extinction levels encountered in 1994, differences in the extinction measurements at 1 μm are within ±10% between 12 and 27 km, increasing at higher and lower altitudes. Differences at 0.45 μm are within ±35% between 13 and 30 km, increasing at lower altitudes. For the lower aerosol extinction conditions of 1995 and 1996, the comparisons indicate that systematic errors contributed to larger relative differences between the instruments. These effects are manifested as “asymmetries” in the Northern Hemisphere versus Southern Hemisphere comparisons, and in the 1 μm versus 0.45 μm comparisons. We suggest that these systematic differences are partly due to altitude registration errors in one or both of the instruments. Average volume densities derived using a principal component analysis technique agreed within about 10% at high northern latitudes between 16 and 27 km, and within about 30% at high southern latitudes. In most cases, surface area density differences were somewhat larger. Although a dedicated validation campaign was not feasible for POAM II, overall the results presented here confirm the validity of the POAM II aerosol measurements for scientific studies.